Multi-user communication in a multi-BSS environment of an 802.11 ax network

ABSTRACT

The invention provides multi-user communication in a MU Uplink transmission opportunity in case of a multi-BSS environment of a wireless network. Resource units with AID=0 or 2045 are available for stations to transmit data to addressee virtual access points (VAPs) other than the VAP having initiated the TXOP. The initiating VAP receiving frames from the resources forwards them to the appropriate addressee VAPs within the same physical AP. Responses may be provided by the addressee VAPs directly to the stations or via the initiating VAP or the representative VAP. This approach increases the opportunities for the stations to access the medium in case of multiple BSSs. Better usage of the MU Uplink OFDMA transmission is also made.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationnetworks comprising a physical access point (AP) and stations organizedinto groups, also known as Basic Service Sets (BSSs), and morespecifically to the transmission of data over a sub-channel or ResourceUnit (RU) forming a transmission opportunity granted to the AP, andcorresponding devices.

The invention finds application in wireless communication networks, inparticular to the access of an 802.11ax composite channel and of OFDMAResource Units forming for instance an 802.11ax channel for Uplinkcommunication towards the AP. One application of the method regardswireless data communication over a wireless communication network usingCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA), thenetwork being accessible by a plurality of station devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.) defines a waywireless local area networks (WLANs) work at the physical and mediumaccess control (MAC) level. Typically, the 802.11 MAC (Medium AccessControl) operating mode implements the well-known DistributedCoordination Function (DCF) which relies on a contention-based mechanismbased on the so-called “Carrier Sense Multiple Access with CollisionAvoidance” (CSMA/CA) technique.

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices (or stations) used in dense deployment scenarios.

In this context, multi-user (MU) transmission has been considered toallow multiple simultaneous transmissions to/from different stations(i.e. users) registered with the AP, in both downlink (DL) and uplink(UL) directions from/to the AP, during a transmission opportunitygranted to the AP over a 20 MHz (or more) communication channel.

In the uplink, multi-user transmissions are used to mitigate thecollision probability. This is because multiple non-AP stations areallowed to transmit simultaneously.

To actually perform such multi-user transmission, it has been proposedto split a granted communication channel (or transmission opportunitygranted to the AP) into sub-channels, also referred to as resource units(RUs), that are usually shared in the frequency domain between multipleusers (non-AP stations/nodes), based for instance on OrthogonalFrequency Division Multiple Access (OFDMA) technique.

Both multi-user Downlink OFDMA and Uplink OFDMA mechanisms offeroverhead reduction as key benefit.

To perform multi-user (MU) Uplink OFDMA transmission, the AP sends acontrol frame, known as Trigger Frame (TF), to the stations prior theycan access one RU of the MU Uplink OFDMA transmission, either assignedto them or randomly accessible through contention. RUs are assigned tospecific stations in the TF, using the AIDs associated with the stationsupon registration with the AP. Random RUs are signalled in the TF usingan AID set to specific value, and may be accessed by any stationregistered with the AP.

This describes how the stations are managed within a single BSS handledby the AP with which they have registered.

In the 802.11 standard, each BSS is uniquely identified using a specificbasic service set identification, BSSID. For a BSS operating ininfrastructure mode, the specific BSSID is usually a 48-bit MAC addressof the access point. The specific BSSID is the formal name of the BSSand is always associated with only one BSS.

Together with the specific BSSID, each BSS has its own service setidentification, SSID, which is an informal (human) name of the BSS(since this own SSID identifier is often entered into devices manuallyby a human user).

Recent developments provide that a single physical AP can operate as themaster stations of a plurality of BSSs, i.e. of a plurality ofindependent groups of stations. This avoids using one physical AP perBSS or WLAN. It also makes it possible to use the same primary channelfor all BSSs, thereby avoiding channel interference problems. In such acase, it is said that the physical AP supports Multi-BSSIDfunctionality. For the non-AP stations, nothing changes.

When a physical AP supports the multi-BSSID functionality, the operatingscheme is performed through so-called virtual access points (virtual APsor VAPs) instantiated at the physical AP.

A Virtual AP is a logical entity that resides within the physical AccessPoint (AP) to manage one of the BSSs. Each VAP appears to the non-APstations as an independent access point with its own unique SSID.

To implement virtual APs, multiple BSSIDs are used with associatedSSIDs. The BSSIDs for the VAPs in the physical AP are usually generatedfrom a base BSSID specific to the underlying physical AP, usually thebase MAC address of the AP.

The terms Virtual AP (VAP), specific BSSID, BSS and SSID can be usedsynonymously to designate one of the groups or cells of stations managedby the physical AP.

Depending on the context, specific BSSID and own SSID may further referto the identifier of the corresponding BSS/WLAN, either through a MACaddress (specific BSSID) or an informal (human) name (own SSID).

Providing a plurality of SSIDs (or BSSs) corresponds to providingvarious different networks in a particular area. It can give access todifferent resources and present services which may have differingmanagement or security policies applied. This advantageously allowsvarious categories of user, e.g. staff, students or visitors etc. to beprovided with network services which are appropriate to them.

In conventional 802.11 approaches, only one SSID (or BSS) is advertisedper signalling message such as a beacon frame. As a consequence,multiple beacon frames are used to advertise the SSIDs corresponding tothe virtual APs configured at the physical AP. This solution iscompatible with most 802.11 stations and also allows the SSIDs tosupport different capability sets.

However, as the number of BSSs increases, more channel utilizationresults from such signalling. This downside is further increased becausethe signalling messages are transmitted at low bit rate, usually at thelowest supported data rate so that all clients can receive it.

To improve this situation of increased channel utilization in case ofmultiple BSSs, the IEEE 802.11v Wireless Network Managementspecification defines a mechanism to advertise network information (e.g.security profiles including BSSID/SSID and protection security schemes)of multiple BSSs with a single beacon frame. This can be made by onlyone of the VAPs of the physical AP, namely the “representative” or“transmitted” VAP.

When a physical AP supports the multi-BSSID functionality, the handlingof MU Uplink OFDMA transmission is made independently within each BSS asdescribed above: the corresponding VAP sends a trigger frame identifyingthe concerned BSS (using the corresponding BSSID), thereby providing RUsto the stations of the concerned BSS only.

Things are slightly different with the representative VAP, which mayassign and thus open access to some RUs triggered by a sent triggerframe, to stations not belonging to its respective BSS.

Recently, the 802.11ax task group has proposed a mechanism for the AP toreserve one or more RUs of a MU Uplink OFDMA transmission fornot-yet-associated stations (which are 802.11ax compliant). This is forthese stations to speed up their registration with the AP, bytransmitting request management frames over such reserved RUs (in MUUplink OFDMA mode). The proposed mechanism relies on the use of apredefined AID value equal to 2045 to indicate such random RUs thenot-yet-associated stations can access through contention.

The independence between the BSSs and thus between the associatedgranted MU Uplink OFDMA transmissions makes that each station registeredwith a specific VAP or willing to register with it may have to wait fora long and unknown time before a MU Uplink OFDMA transmission for theappropriate BSS is triggered. This is particularly unsatisfactory duringthe association process of registration with a VAP as the user usuallydoes not want to wait a long time before being connected. Thus, it isdetrimental to user experience.

The current operating mode of the 802.11ax multi-user feature is thusnot fully satisfactory, for at least the above downsides regarding themulti-BSSID functionality.

SUMMARY OF INVENTION

It is a broad objective of the present invention to improve thissituation, i.e. to overcome some or all of the foregoing limitations. Inparticular, the present invention seeks to provide a more efficientusage of the MU Uplink transmission towards the AP in the context ofmultiple BSSs.

In particular, the Multi-User Uplink communication protocol is enhancedto allow the stations of a BSS (or willing to join such BSS) to use RUsprovided during the MU Uplink transmission of another BSS, provided thattheir communications are forwarding to the appropriate virtual AP.

In this context, the present invention proposes enhanced wirelesscommunication methods in a wireless network comprising a physical accesspoint and stations organized into groups, the physical access pointimplementing a plurality of virtual access points, each virtual accesspoint managing a group of the stations and a single one of the virtualaccess points being a representative virtual access point authorized tobroadcast network information about a non-representative virtual accesspoint. Such broadcasting of network information means advertise networkinformation, e.g. security profiles including BSSID/SSID and/orprotection security schemes, of multiple BSSs with a single controlframe, e.g. a beacon frame.

In embodiments, the method comprises following steps, at a transmittingstation willing to transmit data to a second virtual access pointmanaging a second group of stations:

receiving a trigger frame from a first virtual access point over thewireless network, the trigger frame identifying a first group ofstations managed by the first virtual access point different from thesecond group and reserving a transmission opportunity on at least onecommunication channel of the wireless network, the transmissionopportunity including resource units that form the communication channeland that stations access to transmit data during the reservedtransmission opportunity; and

accessing one of the resource units not assigned to a specific stationduring the transmission opportunity and transmitting data intended tothe second virtual access point, over the accessed resource unit to thefirst virtual access point.

From the AP perspective, enhanced wireless communication methods arealso proposed.

In embodiments, the method comprises following steps, at the physicalaccess point:

sending, by a first virtual access point managing a first group ofstations, a trigger frame identifying the first group of stations, toreserve a transmission opportunity on at least one communication channelof the wireless network, the transmission opportunity including resourceunits that form the communication channel and that stations access totransmit data during the reserved transmission opportunity;

in response to the trigger frame, receiving, over one of the resourceunits during the reserved transmission opportunity, data from atransmitting station and addressed to a second (representative ornon-representative, but different) virtual access point managing asecond group of stations, different from the first group identified inthe trigger frame; and

forwarding the received data to the second virtual access point managingthe second group of stations.

By allowing the first VAP to forward received data not intended toitself (instead of discarding them) to a second VAP within the samephysical AP, the present invention makes it possible for the non-APstations to use RUs provided within a BSS different from their targetedBSS (with which they are registered or willing to register).

Non-AP stations may thus access RUs within MU Uplink transmissions moreoften, thereby reducing their waiting time. This is particularlyadvantageous to speed up the association process of registration with aVAP.

Also, there is provided a wireless communication device forming stationin a wireless network comprising a physical access point and stationsorganized into groups, the physical access point implementing aplurality of virtual access points, each virtual access point managing agroup of the stations and a single one of the virtual access pointsbeing a representative virtual access point authorized to broadcastnetwork information about a non-representative virtual access point. Thedevice forming station willing to transmit data to a second virtualaccess point managing a second group of stations and comprises at leastone microprocessor configured for carrying out steps of:

receiving a trigger frame from a first virtual access point over thewireless network, the trigger frame identifying a first group ofstations managed by the first virtual access point different from thesecond group and reserving a transmission opportunity on at least onecommunication channel of the wireless network, the transmissionopportunity including resource units that form the communication channeland that stations access to transmit data during the reservedtransmission opportunity; and

accessing one of the resource units not assigned to a specific stationduring the transmission opportunity and transmitting data intended tothe second virtual access point, over the accessed resource unit to thefirst virtual access point.

Also, there is provided a wireless communication device forming physicalaccess point in a wireless network comprising a physical access pointand stations organized into groups. The device forming physical accesspoint comprises at least one microprocessor configured for implementinga plurality of virtual access points, each virtual access point managinga group of the stations and a single one of the virtual access pointsbeing a representative virtual access point authorized to broadcastnetwork information about a non-representative virtual access point. Themicroprocessor is further configured for carrying out steps of:

sending, performed by a first virtual access point managing a firstgroup of stations, a trigger frame identifying the first group ofstations, to reserve a transmission opportunity on at least onecommunication channel of the wireless network, the transmissionopportunity including resource units that form the communication channeland that stations access to transmit data during the reservedtransmission opportunity;

in response to the trigger frame, receiving, over one of the resourceunits during the reserved transmission opportunity, data from atransmitting station and addressed to a second virtual access pointmanaging a second group of stations, different from the first groupidentified in the trigger frame; and

forwarding the received data to the second virtual access point managingthe second group of stations.

Optional features of these embodiments are defined in the appendedclaims with reference to methods. Of course, same features can betransposed into system features dedicated to any device according to theembodiments of the invention.

In some embodiments, the first virtual access point is anon-representative virtual access point.

In other embodiments, the steps of receiving and forwarding areperformed by the first virtual access point. In that case, the physicallayer of the physical AP may receive the data and transmit them to theVAP having sent the trigger frame, this VAP being in charge ofperforming the appropriate data forwarding. Variants may contemplatehaving the physical layer of the physical AP forwarding (orbroadcasting) the received data to each and every VAP implemented at thephysical AP.

In some embodiments, any station registering with a virtual access pointis associated with a unique association identifier used by the virtualaccess point to assign, to the station, a resource unit in atransmission opportunity granted to the virtual access point, and

the resource unit conveying the data of the transmitting station isassigned to an association identifier not associated with a specificstation.

It means that a station willing to transmit data to another BSS(different from the one for which the TF has been sent) may use RUshaving such AID not associated with a specific station. This makes itpossible for the stations to easily identify which RUs can be used foranother BSS.

In specific embodiments, the association identifier not associated witha specific station takes a first AID value, for instance equal to 0, tosignal a resource unit in which any station already registered with anyvirtual access point implemented by the physical access point cantransmit data. This makes the processing of the data to be forwarded bythe first VAP easier, as they are concentrated over the RUs with thespecific first AID value.

In some embodiments, the transmitted data include a data frame intendedto the second virtual access point. A data frame is not dedicated tosignalling, e.g. network signalling (such as management frames of802.11) and communication signalling (such as control frames of 802.11).

In other specific embodiments, the association identifier not associatedwith a specific station takes a second AID value, for instance equal to2045, to signal a resource unit in which only a station not yetregistered with one of the virtual access points can transmit data. Thismakes it possible for the stations to speed up, with no additional cost,their registration with any VAP, and not only with the VAP having sentthe trigger frame.

Indeed, the transmitted data may include a management frame intended tothe second virtual access point within a procedure of associating thetransmitting station with the second virtual access point.

In some embodiments, the resource unit conveying the data of thetransmitting station is a random resource unit to which stationsrandomly access using contention-based access. Indeed, this makes itpossible for any not-designated station to gain access to the RU, inparticular if the station belongs to another BSS.

In some embodiments, the data include a frame header in which at leastone address field is set to a basic service set identification, BSSID,uniquely identifying the second group of stations (i.e. the secondvirtual access point). Thanks to this indication, the first VAP canquickly determine when forwarding received data (if it is not its ownBSSID) and to which VAP of the same physical AP.

Indeed, the method may further comprise, at the first virtual accesspoint, determining whether a frame header of the received data includesan address field set to the BSSID uniquely identifying the second groupof stations, and forwarding the received data in case of positivedetermining.

According to specific features, the at least one address field includesone or both of a receiver address and a destination address signalled inthe frame header. This makes the invention compliant with theconventional MAC frame format. Furthermore, the frame header may furtherinclude a source address field set to an address of the transmittingstation.

According to another specific feature, the BSSID uniquely identifyingthe second group of stations is a 48-bit MAC address assigned to thesecond virtual access point.

In some embodiments, the method at the AP may further comprise, at thesecond virtual access point:

generating a response to the received data, and

transmitting directly the generated response to the transmittingstation.

It means the response does not use the same transmission path as thedata (no relay through the first VAP is made). This is simple toimplement with low processing by the physical AP.

Correspondingly, the method may further comprise, at the transmittingstation, receiving a response to the transmitted data, directly from thesecond virtual access point.

In variants, the method at the AP may further comprise, at the secondvirtual access point:

generating a response to the received data, and

forwarding the generated response to another (intermediary) virtualaccess point implemented at the physical access point for transmissionto the transmitting station.

Correspondingly, the method may further comprise, at the transmittingstation, receiving a response to the transmitted data, from the secondvirtual access point via another virtual access point implemented at thephysical access point.

For instance, the other virtual access point may be the first virtualaccess point or the representative virtual access point.

In the first case, the first VAP may advantageously use the sametransmission opportunity, thus reducing overall latency. Indeed, the VAPmay provide both MU Uplink and Downlink OFDMA transmissions within thesame TXOP.

In the second case, numerous, possibly all, responses can beconcentrated at the representative VAP, which in turn may efficient usea MU Downlink OFDMA transmission to transmit all the responses shortly.

In this case of response path with relay, a frame header of the responsemay include a receiver address field set to a basic service setidentification, BSSID, uniquely identifying the group of stationsmanaged by the other virtual access point, a transmitter address fieldset to a BSSID uniquely identifying the second group of stations managedby the second virtual access point and a destination address field setto an address of the transmitting station.

In some embodiments, the transmitted data include a MAC frame embeddedin an 802.11ax frame.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device, causes the device toperform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and devices.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIG. 2a illustrates the format of a conventional 802.11 MAC frame;

FIG. 2b illustrates an exemplary format of a beacon frame;

FIG. 2c illustrates an exemplary format of a Multiple BSSID element usedin beacon frames;

FIG. 3 illustrates an exemplary sequence of management frames allowing anot-yet-associated station to discover and register with a given AccessPoint;

FIG. 4 illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 5 illustrates an example of 802.11ax MU Uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) as knownin the art;

FIG. 6 illustrates a sequence diagram of data exchange between a non-APstation and a VAP via the MU Uplink OFDMA access scheme as defined in802.11ax;

FIG. 7 shows a schematic representation a communication device inaccordance with embodiments of the present invention;

FIG. 8 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIG. 9 illustrates, using a flowchart, exemplary operations at a non-APstation according to embodiments of the invention;

FIG. 10 illustrates, using a flowchart, corresponding exemplaryoperations at a virtual AP according to embodiments of the invention;

FIG. 11 illustrates a sequence diagram of corresponding data exchange in802.11ax from a non-AP station to a physical AP supporting theMulti-BSSID functionality according to embodiments of the invention;

FIG. 12 illustrates, using a flowchart, exemplary operations at anaddressee virtual access point according to embodiments of theinvention;

FIG. 13 illustrates sequence diagrams of corresponding data exchange in802.11ax from the addressee VAP according to various embodiments of theinvention; and

FIG. 14 illustrates an exemplary sequence of management frames allowinga station to discover and associate with a virtual AP according toembodiments of the invention.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source or transmitting station, including the AP, first attemptsthrough the physical mechanism, to sense a medium that has been idle forat least one DIFS (standing for DCF InterFrame Spacing) time period,before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source station continues to wait until the radio mediumbecomes idle.

To access the medium, the station starts a countdown backoff counterdesigned to expire after a number of timeslots, chosen randomly in acontention window range [0, CW], CW (integer) being also referred to asthe Contention Window size and defining the upper boundary of thebackoff selection interval (contention window range). This backoffmechanism or procedure is the basis of the collision avoidance mechanismthat defers the transmission time for a random interval, thus reducingthe probability of collisions on the shared channel. After the backofftime period, the source station may send data or control frames if themedium is idle.

One problem of wireless data communications is that it is not possiblefor the source station to listen while sending, thus preventing thesource station from detecting data corruption due to channel fading orinterference or collision phenomena. A source station remains unaware ofthe corruption of the data frames sent and continues to transmit theframes unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positiveacknowledgement (ACK) of the sent data frames by the receiving stationif the frames are received with success, to notify the source stationthat no corruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame,immediately after a period of time called Short InterFrame Space (SIFS).

If the source station does not receive the ACK within a specified ACKtimeout or detects the transmission of a different frame on the channel,it may infer data frame loss. In that case, it generally reschedules theframe transmission according to the above-mentioned backoff procedure.

FIG. 2a illustrates the format of a conventional 802.11 MAC frame.

An 802.11 MAC frame contains a MAC header (fields 201 to 207), a FrameBody 208, and a Frame Check Sequence (FCS) 209.

The MAC header includes the following fields: a Frame Control field 201to indicate that the type and subtype of the frame: data frame,management frame (beacon, authentication, association frame subtype); aduration field 202; a sequence control field 206.

In addition, it may contain up to four address fields: a first addressfield 203, referred to as address 1 field, a second address field 204,referred to as address 2 field, a third address field 205, referred toas address 3 field and a fourth address field 207, referred to asaddress 4 field. The meaning of these address fields varies from oneframe type to the other, and the content of each one is one from aSource Address (SA) corresponding to a 48-bit identifier that identifiesthe source of the current transmission of the frame, a DestinationAddress (DA) corresponding to a 48-bit IEEE MAC identifier thatidentifies the final recipient of the frame, a Receiver Address (RA)corresponding to a 48-bit IEEE MAC identifier that identifies the nextimmediate recipient of the frame, a Transmitter Address (TA)corresponding to a 48-bit IEEE MAC identifier that identifies thewireless interface that transmitted the frame onto the wireless medium,and a Basic Set Service Set ID (BSSID) corresponding to a 48-bitidentifier that identifies the Basic Service Set of the VAP considered.

If the 802.11 MAC frame is a data frame, the content of each addressfields depends on the type of transmission (uplink or downlink).

In particular, for an uplink transmission from a non-AP station to aVAP, the transmitted data frame sets the address fields as following:address 1 field is set to RA(=BSSID), address 2 field is set to TA(=SA), address 3 is set to DA, and address 4 is not used.

For a downlink transmission from a VAP to a non-AP station, thetransmitted data frame sets the address fields as following: address 1field is set to RA(=DA), address 2 field is set to TA (=BSSID), address3 is set to SA, and address 4 is not used.

This is summarized below:

Transmission mode Address 1 Address 2 Address 3 Address 4 Uplink: STA toAP RA = BSSID TA = SA DA Not used Downlink: AP to STA RA = DA TA = BSSIDSA Not used

On the other hand, if the 802.11 MAC frame is a management frame, thecontent of each address fields is set as following: address 1 field isset to DA, address 2 field is set to SA, address 3 is set to BSSIDidentifying the BSS in which the management occurs.

Address 1 Address 2 Address 3 Address 4 DA SA BSSID Not used

Back to FIG. 1, in IEEE 802.11 standards, the AP and the stationsregistered with it are referred together as a basic service set (BSS),each BSS being identified by a network identifier referred to as basicset identifier (BSSID).

The AP may advertise information about the WLAN (characteristics of theconnection offered to the BSS members) using management frames, known asbeacon frames. Note that a beacon frame can also be used by stations inan independent BSS (IBSS), i.e. an ad-hoc network that contains noaccess point. As an example, some stations may act as a soft-AP(software implemented), that is to say implementing all thefunctionalities of an IEEE 802.11 Access Point but in an ad-hoc ortransient connection mode typically for a specific purpose (e.g.document sharing during a meeting or multiple-player computer games).

FIG. 2b illustrates an exemplary format of such a beacon frame (otherformats may exist).

Illustrated beacon frame 230 contains 24 bytes of MAC header (fields 201a to 206 a), 0 to 2312 bytes of Frame Body 208 a, and four bytes ofFrame Check Sequence (FCS) 209 a. The MAC header includes the followingfields: a frame control field 201 a to indicate that the frame is amanagement frame of beacon subtype, a duration field 202 a set to zero,a DA field 203 a set to broadcast value FF:FF:FF:FF:FF:FF, a SA field204 a and a BSSID field 205 a.

The Frame Body is a field of variable length and consists of two sets offields: fields that are mandatory 210, followed by optional fields inthe form of Information Elements (IEs) 211.

Mandatory information in field 210 may contain a Timestamp representingthe time at the access point, which is the number of microseconds the APhas been active, and allowing synchronization between non-AP stations ina BSS; Beacon Interval representing the number of time units (TUs)between successive target beacon transmission times (TBTTs); andcapability Info to indicate requested or advertised optionalcapabilities and Supported Rates fields.

All Information Elements in field 211 share a common general formatconsisting of a 1-byte Element ID field, a 1-byte Length field, anoptional 1-byte Element ID Extension field, and a variable-lengthelement-specific Information field. Each information element isidentified by the contents of the Element ID and, when present, ElementID Extension fields as defined in the 802.11 standard. The Length fieldspecifies the number of bytes following the Length field.

Back to FIG. 1, since 802.11v, IEEE 802.11 Baseline spec supports theMulti-BSSID functionality where a single physical AP implements multipleAPs, also known as “virtual APs” or VAP, to provide multiple local WLANs(or BSSs). In particular, such Multi-BSSID functionality allows forinstance the representative VAP to send only one beacon frame toadvertise network information about n non-representative virtual AP,instead of having each VAP sending its own beacon frame (thus n beaconframes on the medium).

In FIG. 1, the physical AP 110 supports multiple BSSs and thus implementtwo or more VAPs to manage two or more respective WLANs (or BSSs), i.e.two or more groups of stations. Each BSS has to be uniquely identifiedby a specific basic service set identification, BSSID.

In the Figure, the physical AP 110 implements two virtual APs, virtualAP 1 VAP-1 (110A) having MAC address MAC1 as specific BSSID to manage afirst WLAN (BSS) with “guest” as SSID, and virtual AP 2 VAP-2 (110B)having MAC address MAC2 as specific BSSID to manage a second WLAN (BSS)with “Employee” as SSID. The security for each WLAN may be different,i.e. WEP and WPA. Of course more WLANs can be implemented, requiring acorresponding number of virtual APs to be implemented in the physicalAP.

Some stations can register with VAP-1 and thus join the first WLAN“guest”, while other stations can simultaneously register with VAP-2 andthus join the second WLAN “Employee”.

An AP device that supports multiple BSSIDs includes two types of virtualAPs. The first one is referred to as “transmitted AP” or “representativeAP”. Its BSSID is referred to as transmitted BSSID. It takes the primaryrole to transmit Multiple BSSID elements in beacon and probe responseframes. For a given physical AP, only one virtual AP is designated astransmitted AP.

The second type of virtual APs is referred to as “non-representative AP”or “non-transmitted AP”. Its BSSID is referred to as non-transmittedBSSID. The non-representative APs correspond to other virtual APs whichshall not broadcast beacon frames with Multiple BSSID elements. Howeverthey may broadcast beacon frames specific to their own BSS, i.e. withoutMultiple BSSID elements, in order to associate legacy STAs (stations notimplementing IEEE 802.11v) with itself.

Such beacon frame with multiple BSSID elements may be of the type shownin FIG. 2b in which the frame body 211 includes one or more of suchBSSID elements to advertise about a plurality of BSSs. The SA 204 a andBSSID 205 a fields of the beacon frame are thus sets to the MAC addressof the representative virtual AP transmitting the beacon frame.

A Multiple BSSID information element is defined in such single beaconframe to carry the common, inherited information element values of allof the BSSIDs and the unique information elements of thenon-representative BSSIDs (non-representative VAPs). Any station canthus derive the BSSIDs of the non-representative VAPs from the MultipleBSSID information element.

FIG. 2c illustrates an exemplary format of a Multiple BSSID element.

The multiple BSSID information element, referenced 211 a, comprises a1-byte MAX BSSID indicator field 220 and a variable length OptionalSub-elements field 221. The MAX BSSID Indicator field is ‘n’, where2^(n) is the maximum number of BSSIDs supported by the physical accesspoint 110, including the representative BSSID. Optional Sub-elementsfield 221 contains zero or more sub-elements in its Data field, such asfor example the “non-representative BSSID profile” sub-element (eachadvertising network information of a non-representative BSS).

A “non-representative BSSID Profile” is identified by a Sub-element IDof value 0, and shall include the SSID and multiple BSSID-indexsub-elements for each of the supported BSSIDs. It may include aCapabilities field followed by a variable number of informationelements.

The beacon frame may include two or more Multiple BSSID elementscontaining elements for a given BSSID index.

When a station receives a beacon frame with a Multiple BSSID elementthat consists of a non-representative BSSID profile with only themandatory elements (Capability element, SSID and multiple BSSID-index),the station may inherit the complete profile from a previously receivedbeacon frame.

All MAC addresses identifying the virtual APs are generated based on (or“derive from”) a base MAC address specific to the physical access point,usually the base 48-bit MAC address of AP 110. For instance MAC_(i) (‘i’being a BSS index) used as specific BSSID(i) for virtual AP_(i) isgenerated as follows, from the base MAC address BASE_BSSID:MAC_(i)=BSSID(i)=(BASE_BSSID modified to set the n LSBs to zero)|((nLSBs of BASE_BSSID)+i)mod2{circumflex over ( )}n)where LSB refers to the least significant bits, “n” is an AP parameter(integer) defining the maximum number (about 2^(n)) of possible specificBSSIDs, and ‘|’ operator is an XOR operator. The specific BSSID(i)s thusdiffer from one another by their n LSBs. The 48-n MSBs of the generatedspecific BSSIDs are all similar to the corresponding bits of BASE_BSSID.

The same non-AP station can join two WLANs simultaneously only if it hastwo separate WLAN interfaces (e.g. wifi network cards). In that case,the device is considered as two stations in the network, each stationbeing registered with only one WLAN at a time.

For the stations to be aware of available WLANs (or BSSs) and of theinformation defining them (for instance corresponding SSID or SSIDs,corresponding specific BSSID or BSSIDs, communication mode includingInfrastructure or Ad-Hoc, protection security schemes used includingOpen, WEP, WPA-PSK or 802.1X, support transmission rates used, channelin operation, and any optional Information Elements), the VAPs send somecontrol or management frames, including beacon frames and probe responseframes which have substantially the same content.

FIG. 3 illustrates an exemplary sequence of management frames allowing anot-yet-associated station to discover and register with a given AccessPoint. It comprises three phases: WLAN discovery, authentication andassociation, at the end of which the station enters into anauthenticated and associated state with the AP. Note that the stationmay be currently associated with a first VAP (i.e. belonging to a firstWLAN) and willing to join a second WLAN.

802.11 networks make use of a number of options for the first phase of802.11 probing or discovering. For instance, for an enterprisedeployment, the search for a specific network may involve sending aprobe request frame out on multiple channels that specifies the networkname (SSID) and bit rates.

More generally, prior to association with the VAP, the stations gatherinformation about the VAPs (or BSSs) by scanning the channels one by oneeither through passive scanning or active scanning.

In the passive scanning mode, the station scans through successivelyeach 20 MHz channel and waits to listen for beacon frames (declaring oneor more SSIDs) on the scanned channel, regardless of whether thestations has already connected to a specific SSID before or not.

In the active scanning mode, the stations send out probe request frames310 on each wireless 20 MHz channel. The probe request frames maycontain the SSID of a specific WLAN that the station is looking for orthe probe request frames may not contain a specific SSID meaning thestation is looking for “any” SSID in the vicinity of the station.

In response to receiving a probe request frame, the VAP checks whetherthe station has at least one common supported data rate or not. If thereis a compatible data rate, the VAP responds with a probe response frame320, the content of which is similar to a beacon frame: advertising ofthe SSID (wireless network name), of supported data rates, of encryptiontypes if required, and of other 802.11 capabilities of the VAP.

An acknowledgment frame 330 may be sent by the station, in response toreceiving the probe response frame 320.

It is also common for a station that is already associated with a VAP tosend probe request frames regularly onto other wireless channels tomaintain an updated list of available WLANs with best signal strengths.Thanks to this list, when the station can no longer maintain a strongconnection with the VAP, it can roam to another VAP with a better signalstrength using the second and third phases of the association procedure.

The second phase is the 802.11 authentication once a WLAN to join hasbeen chosen by the station. In particular, the station chooses acompatible WLAN from the probe response frames it receives.

802.11 was originally developed with two authentication mechanisms: thefirst authentication mechanism, called “open authentication”, isfundamentally a NULL authentication where the station says “authenticateme” and the VAP responds with “yes”. This is the mechanism used inalmost all 802.11 deployments; the second authentication mechanism,namely the WEP/WPA/WPA2, is a shared key mechanism that is widely usedin home networks or small Wi-Fi deployments and provides security.

During the 802.11 authentication phase, the station sends a low-level802.11 authentication request frame 340 to the selected VAP setting, forinstance, the authentication to open and the sequence to 0x0001. The VAPreceives the authentication request frame 340 and responds to thestation with an authentication response frame 350 set to open indicatinga sequence of 0x0002.

Note that some 802.11 capabilities allow a station to low-levelauthenticate to multiple VAPs without being associated with them (i.e.without belonging to corresponding WLANs). This speeds up the wholeassociation procedure when the station moves between VAPs or APs.Indeed, while a station can be 802.11 authenticated to multiple VAPs, itcan only be actively associated and transferring data through a singleVAP or AP at a time.

Next, the station has to perform actual association with the VAP fromthe low level authentication step. This is the next phase of actual802.11 association by which the station actually joins the WLAN cell.This stage finalizes the security and bit rate options and establishesthe data link between the station and the VAP. The purpose of this finalexchange is for the station to obtain an Association Identifier (AID) tobe used to access the medium and send data within the joined WLAN.

Note that the station may have joined a first network and may roam fromone VAP to another within the physical network. In that case, theassociation is called a re-association.

Once the station determines which VAP (i.e. WLAN) it would like to beassociated with, the station sends an association request frame 360 tothe selected VAP. The association request frame contains chosenencryption types if required and other compatible 802.11 capabilities.

If the elements in the association request frame match the capabilitiesof the VAP, the VAP creates an Association ID (AID) for the station andresponds with an association response frame 370 with a success messagegranting network access to the station. Note that the AID has to beunique within the same physical AP, meaning the VAPs share the samerange of AIDs.

Now the station is successfully associated with the VAP, data transfercan begin in the chosen WLAN using the physical medium.

Note that when a VAP receives a data frame from a station that isauthenticated but not yet associated, the VAP responds with adisassociation frame placing the station into an authenticated butun-associated state. It results that the station must re-associateitself with the VAP to join the corresponding WLAN.

The probe response frame 320, authentication request/response frames 340and 350 and association request/response frames 360 and 370 are unicastmanagement frames emitted in an 802.11 legacy format, known as a singleuser (SU) format. This is a format used for point-to-point communication(here between a VAP and the station). Each of these unicast managementframes is acknowledged by an ACK frame 330.

As indicated above, all the management frames (310, 320, 340, 350, 360,370) and the ACK frames (330) use the lowest common rate supported byboth the station and the VAP (e.g. 24 mbps or less).

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac and later versions(802.11ax for instance) implement larger bandwidth transmission throughmulti-channel operations. FIG. 4 illustrates an 802.11ac channelallocation that supports composite channel bandwidth of 20 MHz, 40 MHz,80 MHz or 160 MHz, by aggregating 20 MHz component channels (400-1 to400-8).

A station (including the AP) is granted a transmission opportunity(TxOP) through the enhanced distributed channel access (EDCA) mechanismon a 20 MHz channel, referred to as “primary channel” (400-3) shared byall stations in the same BSS.

To make sure that no station not belonging to the same BSS uses thesecondary channels, it is provided that the control frames (e.g. RTSframe/CTS frame or trigger frame described below) reserving thecomposite channel are duplicated over each 20 MHz channel of the 40 MHz,80 MHz or 160 MHz composite channel.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, multi-user (MU) transmission features have beenintroduced, that allow multiple simultaneous transmissions to differentusers in both downlink (DL) and uplink (UL) directions, once atransmission opportunity has been reserved and granted to the AP.

To actually perform such multi-user transmission, a granted 20 MHzchannel (400-1 to 400-4) is split into at least one sub-channel, butpreferably into a plurality (usually between two to nine) of elementarysub-channels, or “sub-carriers” or “resource units” (RUs) or “trafficchannels”, that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent stations in order to increase competition within a reservedtransmission opportunity TXOP. This may help to reduce contention andcollisions inside 802.11 networks.

In the MU downlink transmission (from the AP or VAP to the stations),the AP can directly send multiple data to multiple stations in the RUs,by simply providing specific indications within the preamble header ofthe PPDU sent during the TXOP, and then sending data in the data field.

Things are different for the MU Uplink transmissions, because the APmust control when and how (in which RU) the stations must emit data.

Contrary to the MU downlink transmission, a trigger mechanism has beenadopted for the AP to trigger MU uplink communications from variousnon-AP stations. This is for the AP to have such control on the stations(for them to determine the Resource Units allocation) and to signalmedium occupation to legacy stations (i.e. non-802.11ax stations) forthem to set their NAV.

As shown in the example of FIG. 5, the AP sends a trigger frame (TF) 530to the targeted 802.11ax stations to reserve a transmission opportunityTXOP 540.

Based on an AP's decision, the trigger frame TF may define a pluralityof resource units (RUs) 510. The multi-user feature of OFDMA allows theAP to assign different RUs to different stations in order to increasecompetition.

The trigger frame 530 may define “Scheduled” RUs, which may be reservedby the AP for certain stations in which case no contention for accessingsuch RUs is needed for these stations. Such scheduled RUs and theircorresponding scheduled stations are indicated in the trigger frame (byassociating the AID provided to the station by the AP with the RUconcerned). This explicitly indicates the station that is allowed to useeach Scheduled RU. Such transmission mode is concurrent to theconventional EDCA mechanism.

A non-representative VAP may only assign Scheduled RUs to stationsalready registered with it. On the other hand, the representative VAPmay also assign Scheduled RUs to stations registered with other VAPs(i.e. not belonging to its own BSS) implemented in the same physical AP.

The trigger frame TF 530 may also define “Random” RUs, in addition or inreplacement of the “Scheduled” RUs. The Random RUs can be randomlyaccessed by stations. In other words, Random RUs designated or allocatedby the AP in the TF may serve as basis for contention between stationswilling to access the communication medium for sending data. The randomRUs are signalled in the TF 530 by associating a specific reserved AIDwith these RUs. For instance, an AID equal to 0 is used to identifyrandom RUs available for contention by stations associated with the APemitting the trigger frame (i.e. belonging to the same BSS). On theother hand, an AID equal to 2045 may be used to identify random RUsavailable for contention by stations not yet associated with the AP

Note that several random RUs with AID=0 and/or with AID=2045 may beprovided by the same TF.

A random allocation procedure may be considered for 802.11ax standardbased on an additional backoff counter (OFDMA backoff counter, or OBOcounter or RU counter) for random RU contention by the 802.11ax non-APstations, i.e. to allow them for performing contention between them toaccess and send data over a Random RU. The RU backoff counter isdistinct from the classical EDCA backoff counters (as defined in 802.11eversion). However data transmitted in an accessed OFDMA RUs 510 isassumed to be served from same EDCA traffic queues.

The RU random allocation procedure comprises, for a station of aplurality of 802.11ax stations having an positive RU backoff value(initially drawn inside an RU contention window range), a first step ofdetermining, from a received trigger frame, the sub-channels or RUs ofthe communication medium available for contention (the so-called “randomRUs”, either identified by a value 0 for already-associated stations ora value 2045 for not-yet-associated stations), a second step ofverifying if the value of the RU backoff value local to the consideredstation is not greater than the number of detected-as-available randomRUs, and then, in case of successful verification, a third step ofrandomly selecting a RU among the detected-as-available RUs to then senddata. In case the second step is not verified, a fourth step (instead ofthe third) is performed in order to decrement the RU backoff counter bythe number of detected-as-available random RUs.

As one can note, a station having no Scheduled RU is not guaranteed toperform OFDMA transmission over a random RU for each TF received. Thisis because at least the RU backoff counter is decremented upon eachreception of a Trigger Frame by the number of proposed Random RUs,thereby differing data transmission to a subsequent trigger frame(depending of the current value of the RU backoff number and of thenumber of random RUs offered by each of further received TFs).

The stations use the Scheduled and/or Random RUs to transmit data, inparticular MAC data frames during TXOP 540.

In response to the data transmission, the AP sends a Multi-User BlockAcknowledgment frame 550 to acknowledge the data received on each RU.

The MU Uplink (UL) medium access scheme, including both scheduled RUsand random RUs, proves to be very efficient compared to conventionalEDCA access scheme, especially in dense environments as envisaged by the802.11ax standard. This is because the number of collisions generated bysimultaneous medium access attempts and the overhead due to the mediumaccess are both reduced.

Such functioning when the multiple BSS feature is implemented isexplained now with reference to FIG. 6 which illustrates a sequencediagram of data exchange between a non-AP station and a VAP via the MUUplink OFDMA access scheme as defined in 802.11ax.

Non-AP station 610 is assumed to be associated with non-representativeVAP 620 (corresponding to the BSSID #2) or is intended to be associatedwith it.

First, the station waits for the reception of a trigger frame 530 fromVAP 620 to transmit data via the MU Uplink OFDMA access scheme.

Then, comes the time when VAP 620 sends a trigger frame 650 which isreceived by non-AP station 610.

Non-AP station 610 analyses trigger frame 650 to determine whether ornot it can send data (an 802.11 MAC data or management frame) in adedicated RU either scheduled (RU identified according to the AID ofstation 610) or random (according to the RU random allocation proceduredescribed above). In case of positive determining, station 610 builds an802.11 MAC frame as shown in FIG. 2 a.

If the 802.11 MAC frame to be constructed is a data frame, address 1field (RA/BSSID) is set to the 48-bit IEEE MAC address of VAP 620, i.e.to BSSID #2; address 2 field (TA/SA) is set to the 48-bit IEEE MACaddress of station 610 and address 3 (DA) is set to the 48-bit IEEE MACaddress of the final station to which the data provided in the payloadpart 308 are intended.

If the 802.11 MAC frame to be constructed is a management frame, address1 field (DA) is set to the 48-bit IEEE MAC address of VAP 620, i.e. toBSSID #2, address 2 field (SA) is set to the 48-bit IEEE MAC address ofstation 610 and address 3 (BSSID) is set also to the 48-bit IEEE MACaddress of VAP 620, i.e. to BSSID #2.

Constructed MAC frame 660 is then sent in the dedicated RU to VAP 620.

In case of MAC frame 660 is a request from station 610 to VAP 620, VAP620 may provide a response by sending a response frame 670 to station610.

If response frame 670 is a data frame, address 1 field (RA/BSSID) is setto the 48-bit IEEE MAC address of VAP 620, i.e. to BSSID #2; address 2field (TA/SA) is also set to the 48-bit IEEE MAC address of VAP 620,i.e. to BSSID #2 and address 3 (DA) is set to the 48-bit IEEE MACaddress of station 610.

If response frame 670 is a management frame, address 1 field (DA) is setto the 48-bit IEEE MAC address of station 610, address 2 field (SA) isset to the 48-bit IEEE MAC address of VAP 620, i.e. to BSSID #2 andaddress 3 (BSSID) is also set to the 48-bit IEEE MAC address of VAP 620,i.e. to BSSID #2.

The process of FIG. 6 happens as soon as a trigger frame 530/650 isreceived by station 610 from VAP 620. However, the waiting time beforereceiving such a trigger frame may be important, in particular in densenetworks where a large number of VAPs (or BSSs) are implemented by thephysical AP. Indeed, the other VAPs may be granted TXOPs before VAP 620actually accesses the medium through conventional EDCA and sends triggerframe 620.

This waiting time may become detrimental to user experience, forinstance regarding real-time applications (data are sent too rarely) orregarding the association process by which a user station may join aWLAN (the users do not accept waiting for a long time in such process).

These various drawbacks of the current version of 802.11ax show that amore efficient usage of the MU Uplink transmission is sought when themulti BSS feature is enabled.

The inventors have contemplated allowing the stations to use specificRUs in MU Uplink transmissions provided by VAPs different from their ownVAP (with which they have registered) to provide more frequent access tothe medium for these stations. An idea of the inventors to make thisapproach workable is to configure the VAP receiving the MU Uplinktransmissions (i.e. the VAP having sent the corresponding trigger frame)to forward data received from a station belonging to another BSS to theappropriate other VAP.

A first virtual access point managing a first group of stations thussends a trigger frame identifying the first group of stations, toreserve a transmission opportunity on at least one communication channelof the wireless network, the transmission opportunity including resourceunits that form the communication channel and that stations access totransmit data during the reserved transmission opportunity.

A transmitting station willing to transmit data to a second virtualaccess point managing a second (and different) group of stations thusreceives the sent trigger frame, accesses one of the resource units notassigned to a specific device during the transmission opportunity andtransmits data (e.g. data frame or management frame) intended to thesecond virtual access point, over the accessed resource unit to thefirst virtual access point.

In response to the trigger frame, the first virtual access point thusreceives, over one of the resource units during the reservedtransmission opportunity, data from the transmitting station andaddressed to the second virtual access point managing a second group ofstations, different from the first group identified in the triggerframe; and decides to forward the received data to the second virtualaccess point managing the second group of stations.

The first virtual access point may thus forward data received over aScheduled RU used by a station registered with another VAP, but alsoforward data generally received over a Random RU used by a stationregistered with another VAP or willing to register with such other VAP.

Specific and exemplary implementations of these mechanisms are describedin details below.

It results that a station, already registered or not with a VAP, cancommunicate more frequently with its VAP through MU Uplink transmissionstriggered by any VAP, be it a non-representative or a representativeVAP.

MU Uplink transmission is thus significantly improved compared to knowncurrent 802.11ax requirements.

FIG. 7 schematically illustrates a communication device 700, either anon-AP station 101-107 or the access point 110, of the radio network100, configured to implement at least one embodiment of the presentinvention. The communication device 700 may preferably be a device suchas a micro-computer, a workstation or a light portable device. Thecommunication device 700 comprises a communication bus 713 to whichthere are preferably connected:

-   -   a central processing unit 711, such as a microprocessor, denoted        CPU;    -   a read only memory 707, denoted ROM, for storing computer        programs for implementing the invention;    -   a random access memory 712, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 702 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ax protocol. The        frames are written from a FIFO sending memory in RAM 712 to the        network interface for transmission or are read from the network        interface for reception and writing into a FIFO receiving memory        in RAM 712 under the control of a software application running        in the CPU 711.

Optionally, communication device 700 may also include the followingcomponents:

-   -   a data storage means 704 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 705 for a disk 706, the disk drive being adapted to        read data from the disk 706 or to write data onto said disk;    -   a screen 709 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 710 or        any other pointing means.

The communication device 700 may be optionally connected to variousperipherals, such as for example a digital camera 708, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 700.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 700 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 700 directly or by means of another element of the communicationdevice 700.

The disk 706 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory707, on the hard disk 704 or on a removable digital medium such as forexample a disk 706 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 703, via the interface 702, in order to bestored in one of the storage means of the communication device 700, suchas the hard disk 704, before being executed.

The central processing unit 711 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 704 or in the read only memory 707, aretransferred into the random access memory 712, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 8 is a block diagram schematically illustrating the architecture ofthe communication device 700, either the AP 110 or one of stations101-107, adapted to carry out, at least partially, the invention. Asillustrated, device 700 comprises a physical (PHY) layer block 803, aMAC layer block 802, and an application layer block 801.

The PHY layer block 803 (here an 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancemedium access trigger frames TF 530 (FIG. 5) to reserve a transmissionslot, MAC data and management frames based on a 20 MHz width to interactwith legacy 802.11 stations, as well as of MAC data frames of OFDMA typehaving smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/fromthat radio medium.

The MAC layer block or controller 802 preferably comprises a MAC 802.11layer 804 implementing conventional 802.11ax MAC operations, andadditional blocks 805 and 806 for carrying out, at least partially, theinvention. The MAC layer block 802 may optionally be implemented insoftware, which software is loaded into RAM 712 and executed by CPU 711.

Preferably, additional block 805, referred to as multiple-BSS managementmodule for controlling access to random OFDMA resource units(sub-channels) in case of multiple BSSs, implements the part ofembodiments of the invention that regards non-AP station and/or VAPoperations of device 700.

Additional block 806, referred as to OFDMA module for configuring andupdating the OFDMA-based MU Uplink random access procedure, implementsthe part of embodiments of the invention that regards non-AP stationoperations of device 700. The same block 806 may handle the OFDMA-basedMU Downlink random access procedure for the VAPs.

For instance and not exhaustively, the operations for the VAP mayinclude generating and sending beacon frames sometimes identifying aplurality of groups, instead of a single BSS; generating and sendingtrigger frames providing RUs for stations of one or more other BSSs;processing frames received in such RUs to forward them to appropriateVAPs within the same physical AP; building and sending responses torequests received from stations; processing responses to forward them toanother VAP in the physical AP for efficient transmission to requestingstations.

The operations for a non-AP station may include analyzing trigger framesreceived from VAPs to determine if the station is allowed to access somerandom RUs in the context of multi-BSS, and then to actually access sucha RU to transmit, during MU Uplink OFDMA transmission, frames to otherVAPs via the VAPs having sent the trigger frames.

MAC 802.11 layer 804, multiple-BSS management module 805 and OFDMAmodule 806 interact one with the other in order to process accuratelycommunications over MU Uplink OFDMA RUs provided to multiple BSSsaccording to embodiments of the invention.

On top of the Figure, application layer block 801 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 801 represents all the stacklayers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using variousexemplary embodiments in the context of IEEE 802.11ax by consideringOFDMA RUs dedicated to multiple BSSs.

Although the proposed examples are also mainly described with referenceto the 802.11ax trigger frames and the management frames of the 802.11association process, the present invention is not limited to suchframes.

FIG. 9 illustrates, using a flowchart, exemplary operations at a non-APstation according to embodiments of the invention. FIG. 10 illustrates,using a flowchart, corresponding exemplary operations at a VAP accordingto embodiments of the invention.

FIG. 11 illustrates a sequence diagram of corresponding data exchange in802.11ax from a non-AP station to a physical AP supporting theMulti-BSSID functionality according to embodiments of the invention.

Non-AP station 1101 (implementing the operations of FIG. 9) is assumedto be associated or intended to be associated (in which case its currentstate is non-associated) with VAP 1103, referred to as Virtual AP #2,having BSSID #2. Station 1101 is thus willing to transmit data (e.g.data frame or management frame) to VAP #2.

At step 910, a trigger frame 1110 is received from virtual AP #1 1102corresponding to BSSID #1 (identified by a TA address equal to BSSID #1)which is preferably a non-representative VAP (the representative VAPbeing virtual AP #0). In the state of the art, only the non-AP stationsassociated or intended to be associated with VAP #1 (having BSSID #1)may participate to the MU Uplink OFDMA transmission initiated byreceived trigger frame 1110. Consequently, stations as in the state ofthe art (not implementing the present invention) directly discardtrigger frame 1110.

Note that when a trigger frame is sent by the representative VAP, thenon-AP station does not directly discard the trigger frame, but checkswhether or not one Scheduled RU is assigned to it, in order to use it,if any.

On the contrary, with the present invention, station 1101 analysesreceived trigger frame 1110 at step 920. In particular, the stationchecks whether or not the received trigger frame provides a RU notassigned to a specific station and opened to stations not related to BSS#1 managed by VAP #1, i.e. whether or not trigger frame 1110 hasassigned one or more dedicated/predefined RUs to stations not belongingto BSS #1. This is a Random RU in the meaning that the stations may gainaccess to it using contention.

For instance, such a RU may be identified by a given AID not associatedwith a specific station by the VAPs, referred to as AIDp.

As an example, AID_(p) may take a first AID value, for instance equal to0, to signal a resource unit in which any station already registeredwith any virtual access point implemented by the physical access pointcan transmit data.

As another example, AID_(p) may take a second AID value, for instanceequal to 2045, to signal a resource unit in which only a station not yetregistered with one of the virtual access points can transmit data, i.e.stations willing to register with one of the virtual APs.

By this mechanism, the invention offers new possibilities to stations toparticipate to a MU Uplink transmission initiated (through a triggerframe) by a first virtual AP, even if the stations are associated (orintended to be associated) with another virtual AP.

Step 920 may optionally check whether the identified RU with AID=AID_(p)can be accessed by the station. For instance, the station may apply theRU random allocation procedure described above (are there more randomRUs with AID=AID_(p) than an OBO backoff counter local to the station?)in order to know if it is allowed to use the RU (to transmit the MACdata) in the current MU Uplink OFDMA transmission or if it needs to waitfor a next opportunity of medium access.

In case of positive checking at step 920 (a RU assigned to an AID equalto AIDp has been identified), next step is step 930; otherwise thealgorithm ends.

Through steps 930 and 940, the station “catches” the current MU UplinkOFDMA transmission, although it is not initiated within its own BSS.Consequently the invention allows an access to the medium by thestations to be made faster in order to transmit data.

At step 930, the station builds the MAC frame to be sent withappropriate address fields. Various embodiments may be implemented, eachof which provides that the MAC frame includes a frame header in which atleast one address field is set to a basic service set identification,BSSID, uniquely identifying the second group of stations, i.e. BSSID #2in the present example of FIG. 11.

The embodiments differ from one another in that the at least one addressfield having BSSID #2 in the above example includes one or the other orboth of a receiver address and a destination address signalled in theframe header. Note that the frame header may further include a sourceaddress field set to an address of the station being about to transmitthe data.

According to first embodiments, only the field usually corresponding tothe BSSID of the BSS in which the MU UL OFDMA transmission takes placeis modified by replacing BSSID #1 (because the trigger frame has beensent by VAP #1) by BSSID #2.

In the case of an 802.11 MAC data frame, address 1 field (RA/BSSID) isset to BSSID #2 (instead of BSSID #1), i.e. to the 48-bit IEEE MACaddress of VAP #2 1103, address 2 field (TA/SA) is set to the 48-bitIEEE MAC address of station 1101 (as done conventionally) and address 3(DA) is set to the 48-bit IEEE MAC address of the final station (as doneconventionally).

In case of an 802.11 MAC management frame (such as frames 310, 340,360), address 1 field (DA) is set to the 48-bit IEEE MAC address of thefinal station (as done conventionally), address 2 field (SA) is set tothe 48-bit IEEE MAC address of station 1101 (as done conventionally) andaddress 3 is set to BSSID #2 (instead of BSSID #1), i.e. to the 48-bitIEEE MAC address of VAP #2 1103.

In this way, contrary to the known techniques, a frame with a BSSIDaddress field (address 1 field for data frame and address 3 field formanagement frame) equal to a given BSSID (BSSID #2) is sent during aTXOP initiated by a VAP corresponding to another BSSID (BSSID #1).

Second embodiments regard the case where the final station is the accesspoint itself (which thus not act only as a mere relay to a finalstation). In terms of address fields, it means the DA address fieldshould normally be set to BSSID #1, the VAP initiating the MU UplinkOFDMA transmission.

In the second embodiments, only the field corresponding to the DA ismodified by replacing BSSID #1 by BSSID #2.

In the case of an 802.11 MAC data frame, address 1 field (RA/BSSID) isset to BSSID #1, i.e. to the 48-bit IEEE MAC address of VAP #1 1102having sent the trigger frame (as done conventionally), address 2 field(TA/SA) is set to the 48-bit IEEE MAC address of station 1101 (as doneconventionally) and address 3 (DA) is set to BSSID #2 (instead of BSSID#1), i.e. to the 48-bit IEEE MAC address of VAP #2 1103.

In case of an 802.11 MAC management frame (such as frames 310, 340,360), address 1 field (DA) is set to BSSID #2 (instead of BSSID #1),i.e. to the 48-bit IEEE MAC address of VAP #2 1103, address 2 field (SA)is set to the 48-bit IEEE MAC address of station 1101 (as doneconventionally) and address 3 is set to BSSID #1, i.e. to the 48-bitIEEE MAC address of VAP #1 1102 having sent the trigger frame (as doneconventionally).

Third embodiments combine the first and second embodiments. Thus theyalso regard the case where the final station is the access point itself.

In the third embodiments, both fields corresponding to DA and to BSSIDare modified by replacing BSSID #1 by BSSID #2.

In the case of an 802.11 MAC data frame, address 1 field (RA/BSSID) isset to BSSID #2 (instead of BSSID #1), i.e. to the 48-bit IEEE MACaddress of VAP #2 1103, address 2 field (TA/SA) is set to the 48-bitIEEE MAC address of station 1101 (as done conventionally) and address 3(DA) is also set to BSSID #2 (instead of BSSID #1).

In case of an 802.11 MAC management frame (such as frames 310, 340,360), address 1 field (DA) is set to BSSID #2 (instead of BSSID #1),i.e. to the 48-bit IEEE MAC address of VAP #2 1103, address 2 field (SA)is set to the 48-bit IEEE MAC address of station 1101 (as doneconventionally) and address 3 is also set to BSSID #2 (instead of BSSID#1).

Thanks to the indication of BSSID #2 in the MAC frames received by VAP#1, the latter will be able to decide when processing by its own thereceived MAC frames or when forwarding them to another VAP, as describedbelow.

Next to step 930, step 940 transmits the built frame 1120 over thededicated RU determined at step 920.

Turning now to FIG. 10, VAP #1 receives, at step 1010 and in response tosent trigger frame 1110 and over one of the resource units during thereserved transmission opportunity, a MAC frame from transmitting station1101. In use, VAP #1 received plenty of MAC frames over plenty of RUsrespectively. For instance, the physical AP receiving (at its physicallayer 803) the MAC frame may directly transmit the MAC frame to the VAPhaving transmitted the trigger frame, i.e. to VAP #1 in the presentexample.

The process below is performed for each received MAC frame.

At step 1020, VAP #1 determines whether or not the MAC frame has beenreceived over a RU open to stations not related to BSS #1 managed by VAP#1. In particular, VAP #1 determines whether or not this RU has an AIDequal to an AID not associated with a specific station, such asAID_(p)=0 or 2045.

In case of positive determining, next step is 1030; otherwise theprocess goes to step 1040 to process the MAC frame conventionally.

As the stations (associated or intended to be associated with a VAP) maybelong to any virtual AP implemented by the physical AP and not only toVAP #1 (as in the known techniques), next step 1030 checks whether ornot the MAC frame is to be addressed to a VAP different from VAP #1, forinstance to be addressed to VAP #2 in the above example.

This may comprise, for VAP #1, to determine whether or not a frameheader of the received MAC frame includes an address field set to theBSSID uniquely identifying a second group of stations, i.e. to BSSID #2in the example. In particular, VAP #1 checks address 1 field and/oraddress 3 field according to the embodiments described above.

In case of positive determining, the MAC frame has to be addressed toVAP #2. Thus next step is step 1050. Otherwise, the process goes to step1040.

At step 1050, VAP #1 forwards (internally within physical AP 110reference 1130 in FIG. 11) the received MAC frame to the VAPcorresponding to the BSSID (different from BSSID #1) indicated in theframe header, i.e. to VAP #2 in the example of FIG. 11. Note that forthe forwarding, the address fields of the MAC frame do not need to bemodified.

At that time, VAP #2 1103 receives the MAC frame sent by station 1101,via intermediary VAP #1 1102. It then processes it accordingly. Forinstance, if VAP #2 is a gateway to another (external) network to whicha station identified in the DA address field of the frame headerbelongs, VAP #2 may merely retransmit the MAC frame in said othernetwork to the station identified in the DA address field. In response,VAP #2 may receive other data from this station to be transmitted totransmitting station 1101.

Things are quite similar when the MAC frame is a management frame. Inthat case, VAP #2 may generate by its own a response to the receivedmanagement frame.

Note that the embodiments described above with reference to FIGS. 9 to11 may implement the reception of the MAC frame by the physical AP andthen a transmission of the received MAC frame to VAP #1 having initiallytransmitted the trigger frame. Variants may however be contemplated. Forinstance, the received MAC frame may be broadcast, i.e. forwarded, bythe physical layer 803 of physical AP 110 to each and every VAP itimplements, and each of these VAPs is responsible for locally processingthe MAC frame. This variant reduces latency.

FIG. 12 illustrates, using a flowchart, exemplary operations at theaddressee virtual access point according to embodiments of theinvention. FIG. 13 illustrates sequence diagrams of corresponding dataexchange in 802.11ax from the addressee VAP according to variousembodiments of the invention.

At step 1210, VAP #2 receives the MAC frame from VAP #1 as indicatedabove, said MAC frame having been sent originally by transmitting non-APstation 1101 identified by address SA in the frame header of thereceived MAC frame.

For instance, the DA address filed of the received MAC frame correspondsto BSSID #2, meaning that the received MAC frame corresponds to arequest management frame (310, 340, 360) and that a response is requiredfrom VAP #2.

Next, step 1220 consists for VAP #2 to generate a response (e.g. 320,350, 370) to the received MAC frame. The response may also be the dataprovided by a station in an external network in response to the originalMAC frame 1120.

And VAP #2 1103 transmits the MAC frame response to transmitting station1101 during step 1230. Various embodiments are contemplated in which theMAC frame response is transmitted directly to the transmitting stationor forwarded to another virtual access point implemented at the physicalaccess point for transmission to the transmitting station, said othervirtual access point being possible VAP #1 1102 having sent originaltrigger frame 1110) or the representative virtual access point, notedVAP #0 1104.

In the case with response forwarding, a frame header of the responseinclude a receiver address field set to a basic service setidentification, BSSID, uniquely identifying the group of stationsmanaged by the other virtual access point (forwarding the response), atransmitter address field set to a BSSID uniquely identifying thecurrent VAP, VAP #2 in the example, and a destination address field setto an address of the transmitting station 1101.

Direct-transmission embodiments are illustrated in section (a) of FIG.13. The MAC frame response 1310 is transmitted directly to transmittingstation 1101 using a Single User EDCA transmission as known in 802.11.

In such a case, in the case of an 802.11 MAC data response frame,address 1 field (RA/BSSID) is set to BSSID #2, address 2 field (TA/SA)is set to BSSID #2 and address 3 (DA) is set to the 48-bit IEEE MACaddress of transmitting station 1101.

In the case of an 802.11 MAC management response frame, address 1 field(DA) is set to the 48-bit IEEE MAC address of transmitting station 1101,address 2 field (SA) is set to BSSID #2 and address 3 (BSSID) is alsoset to BSSID #2.

In the direct-transmission embodiments, the transmitting stationreceives a response to the transmitted data, directly from the secondvirtual access point.

Embodiments with a relay by a non-representative VAP, for instance VAP#1 1102 having sent the original trigger frame 1110, are illustrated insection (b) of FIG. 13. The MAC frame response is forwarded (1320) toVAP #1 1102 for transmission to transmitting station 1101.

In such a case, in the case of an 802.11 MAC data response frame,address 1 field (RA/BSSID) is set to BSSID #1 (instead of BSSID #2 whenVAP #2 wishes to send data to a station), address 2 field (TA/SA) is setto BSSID #2 and address 3 (DA) is set to the 48-bit IEEE MAC address oftransmitting station 1101.

In the case of an 802.11 MAC management response frame, address 1 field(DA) is set to the 48-bit IEEE MAC address of transmitting station 1101,address 2 field (SA) is set to BSSID #2 and address 3 is set to BSSID #1(instead of BSSID #2).

In such a case, when VAP #1 1102 receives the MAC response frame, it mayuse, to relay the MAC response frame 1330 to transmitting station 1101,the same TXOP that the TXOP used for the MU Uplink OFDMA transmissionhaving conveyed the MAC request frame 1120. In that way, packet latencyis reduced.

Embodiments with a relay by the representative VAP, namely VAP #0 1104,are illustrated in section (c) of FIG. 13. The MAC frame response isforwarded (1340) to VAP #0 1104 for transmission to transmitting station1101.

In such a case, in the case of an 802.11 MAC data response frame,address 1 field (RA/BSSID) is set to BSSID #0 (instead of BSSID #2 whenVAP #2 wishes to send data to a station), address 2 field (TA/SA) is setto BSSID #2 and address 3 (DA) is set to the 48-bit IEEE MAC address oftransmitting station 1101.

In the case of an 802.11 MAC management response frame, address 1 field(DA) is set to the 48-bit IEEE MAC address of transmitting station 1101,address 2 field (SA) is set to BSSID #2 and address 3 (BSSID) is set toBSSID #0 (instead of BSSID #2).

In such a case, all the MAC response frames are concentrated to therepresentative VAP which in turn may efficient use a MU Downlink OFDMAtransmission to transmit all the responses 1350 together shortly.

In embodiments with a relay, transmitting station 1101 receives aresponse to the transmitted data, from VAP #2 via another VAPimplemented at the physical access point.

The above-described embodiments of the invention may be used bytransmitting station 1101 to perform an association procedure with VAP#2.

FIG. 14 illustrates an exemplary sequence of management frames allowingsuch a station to discover and associate with VAP #2 according toembodiments of the invention.

Station 1101 not yet associated with a VAP receives a beacon frame 1410from representative VAP #0 1104 (corresponding to the BSSID #0). Thebeacon frame 1410 contains the profiles of all VAPs (includingrepresentative and non-representative VAPs) inside Multiple BSSIDelements. In this way, station 1101 is provided with the list of allavailable VAPs and BSSs (and their capabilities which are contained inthe non-transmitted profiles). Station 1101 is able to select one of theVAPs without sending a probe request 310.

In the present example, station 1101 selects VAP #2 1103 (correspondingto BSSID #2).

Next step of the association process is the transmission of anauthentication request frame 340 by station 1101. To do that, station1101 waits for a next opportunity to access the medium, which is hereprovided in an MU Uplink OFDMA transmission initiated by VAP #1.

Thus, station 1101 receives a trigger frame 1420 from VAP #1 1102corresponding to the BSSID #1. Using the teachings of the presentinvention, station 1101 catches this current MU Uplink OFDMAtransmission by applying above step 910 to 940 to select and access anRU with AID=2045 to transmit the authentication request frame 1430.

VAP #1 1102 receives the authentication request frame and forward it(1440) to VAP #2 within the physical AP 110, by applying above steps1010, 1020, 1030 and 1050.

VAP #2 thus receives the authentication request frame 1450 and generates(1460) an authentication response frame 1470 by applying above steps1210 and 1220. The authentication response frame 1470 is sent byapplying above step 1230.

As depicted in FIG. 14, the first embodiment with direct transmission tostation 1101 (FIG. 13a ) is illustrated.

Station 1101 thus receives the authentication response frame 1470.

The next step in the association process is the transmission of theassociation request frame 360 by station 1101 to receive an associationresponse frame 370 from VAP #2. This next step can be performed in asimilar way as described above for the authentication request frame andthe authentication response frame (references 1420 to 1470).

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

The invention claimed is:
 1. A wireless communication method in awireless network comprising a physical access point and stations, thephysical access point implementing a plurality of virtual access points,each virtual access point managing a group of stations, the methodcomprising following steps, at a transmitting station willing totransmit data to a second virtual access point managing a second groupof stations: receiving a trigger frame from a first virtual access pointmanaging a first group of stations different from the second group, thetrigger frame reserving a transmission opportunity on at least onecommunication channel of the wireless network, the transmissionopportunity including resource units that form the communication channeland that stations can access to transmit data during the reservedtransmission opportunity; and accessing one of the resource units duringthe transmission opportunity and transmitting data intended to thesecond virtual access point, over the accessed resource unit to thefirst virtual access point.
 2. The method of claim 1, wherein a singleone of the virtual access points is a representative virtual accesspoint authorized to broadcast network information about anon-representative virtual access point and the first virtual accesspoint is a non-representative virtual access point.
 3. The method ofclaim 1, wherein any station registering with a virtual access point isassociated with a unique association identifier used by the virtualaccess point to assign, to the station, a resource unit in atransmission opportunity granted to the virtual access point, and theresource unit conveying the data of the transmitting station is assignedto an association identifier not associated with a specific station. 4.The method of claim 3, wherein the association identifier not associatedwith a specific station takes a first AID value to signal a resourceunit in which any station already registered with any virtual accesspoint implemented by the physical access point can transmit data.
 5. Themethod of claim 4, wherein the first AID value equals
 0. 6. The methodof claim 3, wherein the association identifier not associated with aspecific station takes a second AID value to signal a resource unit inwhich only a station not yet registered with one of the virtual accesspoints can transmit data.
 7. The method of claim 6, wherein the secondAID value equals
 2045. 8. The method of claim 1, wherein the transmitteddata include a data frame intended to the second virtual access point.9. The method of claim 1, wherein the transmitted data include amanagement frame intended to the second virtual access point within aprocedure of associating the transmitting station with the secondvirtual access point.
 10. The method of claim 1, wherein the resourceunit conveying the data of the transmitting station is a random resourceunit to which stations randomly access using contention-based access.11. The method of claim 1, wherein the data include a frame header inwhich at least one address field is set to a basic service setidentification, BSSID, uniquely identifying the second group ofstations.
 12. The method of claim 11 further comprising, at the firstvirtual access point, determining whether a frame header of the receiveddata includes an address field set to the BSSID uniquely identifying thesecond group of stations, and forwarding the received data in case ofpositive determining.
 13. The method of claim 11, wherein the at leastone address field includes one or both of a receiver address and adestination address signalled in the frame header.
 14. The method ofclaim 13, wherein the frame header further includes a source addressfield set to an address of the transmitting station.
 15. The method ofclaim 11, wherein the BSSID uniquely identifying the second group ofstations is a 48-bit MAC address assigned to the second virtual accesspoint.
 16. The method of claim 1, further comprising, at thetransmitting station, receiving a response to the transmitted data,directly from the second virtual access point or from the second virtualaccess point via another virtual access point implemented at thephysical access point.
 17. The method of claim 1, wherein thetransmitted data include a MAC frame embedded in an 802.11ax frame. 18.A wireless communication method in a wireless network comprising aphysical access point and stations, the physical access pointimplementing a plurality of virtual access points, each virtual accesspoint managing a group of stations, the method comprising followingsteps, at the physical access point: sending, by a first virtual accesspoint managing a first group of stations, a trigger frame to reserve atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that stations can access totransmit data during the reserved transmission opportunity; in responseto the trigger frame, receiving, over one of the resource units duringthe reserved transmission opportunity, data from a transmitting stationand addressed to a second virtual access point managing a second groupof stations, different from the first group of stations; and forwardingthe received data to the second virtual access point managing the secondgroup of stations.
 19. The method of claim 18, wherein the steps ofreceiving and forwarding are performed by the first virtual accesspoint.
 20. The method of claim 18, further comprising, at the secondvirtual access point: generating a response to the received data, andtransmitting directly the generated response to the transmitting stationor forwarding the generated response to another virtual access pointimplemented at the physical access point for transmission to thetransmitting station.
 21. The method of claim 20, wherein the othervirtual access point is the first virtual access point or arepresentative virtual access point.
 22. The method of claim 20, whereina frame header of the response includes a receiver address field set toa basic service set identification, BSSID, uniquely identifying thegroup of stations managed by the other virtual access point, atransmitter address field set to a BSSID uniquely identifying the secondgroup of stations managed by the second virtual access point and adestination address field set to an address of the transmitting station.23. A wireless communication device forming station in a wirelessnetwork comprising a physical access point and stations, the physicalaccess point implementing a plurality of virtual access points, eachvirtual access point managing a group of stations, the device formingstation willing to transmit data to a second virtual access pointmanaging a second group of stations and comprising at least onemicroprocessor configured for carrying out steps of: receiving a triggerframe from a first virtual access point managing a first group ofstations different from the second group, the trigger frame reserving atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that stations can access totransmit data during the reserved transmission opportunity; andaccessing one of the resource units during the transmission opportunityand transmitting data intended to the second virtual access point, overthe accessed resource unit to the first virtual access point.
 24. Awireless communication device forming physical access point andcomprising at least one microprocessor configured for implementing aplurality of virtual access points, each virtual access point managing agroup of stations, the microprocessor being further configured forcarrying out steps of: sending, by a first virtual access point managinga first group of stations, a trigger frame to reserve a transmissionopportunity on at least one communication channel of the wirelessnetwork, the transmission opportunity including resource units that formthe communication channel and that stations can access to transmit dataduring the reserved transmission opportunity; in response to the triggerframe, receiving, over one of the resource units during the reservedtransmission opportunity, data from a transmitting station and addressedto a second virtual access point managing a second group of stations,different from the first group of stations; and forwarding the receiveddata to the second virtual access point managing the second group ofstations.